Cytologic features of metanephric adenoma of the kidney: case report and review of the literature.

Metanephric adenoma (MA) is a rare, benign renal tumor that can be found in individuals of any age. The histological features of this lesion are well known; however, cytological features of this entity have rarely been described. Herein, we present the case of a 37-year-old white woman with multiple endocrine dysfunctions and a renal mass. The diagnosis of metanephric adenoma was suggested as a differential diagnosis during imprint cytology; this diagnosis was later confirmed by core needle biopsy (CNB) and the results of immunostaining. To our knowledge, this is the first time in the literature that the diagnosis of metanephric adenoma was initially suggested on imprint cytologic testing of a CNB. We review the literature regarding the cytologic features and immunohistochemical reactivity of this tumor to raise awareness of this entity among pathologists and to distinguish it from other lesions, such as renal-cell carcinoma, so physicians can use this information to help them avoid calling for an unnecessary radical nephrectomy.